We're going to lock up your cock and we will be taking turns holding the key

Your younger sister would always tease you while growing up for having such a small cock. She would make you jerk off in front of her without even taking off any clothes and you would still cum in less than a minute.

So naturally, you were a little worried when your new girlfriend and your sister started talking more and getting along better. You were really worried that your sister would tell her about your size and she wouldn't want to fuck you. You came home one day to see your fears have been realized. Your gf (riding this guy's cock) and your sister (grinding his face) were out on the deck in the backyard having some fun.

"Hey tiny, your girl and I have been talking and we decided that you are never to have any sex, ever. We're going to lock up your cock and we will be taking turns holding the key. You do remember that I told you a while back that I would do everything I could so that you never felt the inside of a woman. Well, here we are!"

"Oh my god baby, he's so big! He feels so good. Mmmmm... go ahead and stroke your little thing while you watch your girlfriend and your sister have their way with this real man. You can lick us clean when we're done and then we'll lock you up. Listen to your sister. It's for the best, ok baby? We're going to have so much fun with you."